This invention relates to polyphenylene oligomers and polymers and processes for preparing and using the same. Such oligomers and polymers may be useful as dielectric resins in microelectronics fabrication.
Polymer dielectrics may be used as insulating layers between various circuits and layers within circuits in microelectronic devices such as integrated circuits, multichip modules, laminated circuit boards and the like. The microelectronics fabrication industry is moving toward smaller geometries in its devices to enable lower power and faster speeds. As the conductor lines become finer and more closely packed, the requirements of the dielectrics between such conductors become more stringent.
While polymer dielectrics often provide lower dielectric constants than inorganic dielectrics such as silicon dioxide, they often present challenges to process integration during fabrication. For example, to replace silicon dioxide as a dielectric in integrated circuits, the dielectric must be able to withstand processing temperatures during metallization and annealing steps of the process. Preferably, the dielectric material should have a glass transition temperature greater than the processing temperature. The dielectric must also retain the desirable properties under device use conditions. For example, the dielectric should not absorb water which may cause an increase in the dielectric constant and potential corrosion of metal conductors.
For some integration schemes, the oligomer should preferably planarize and gap fill a patterned surface when applied by conventional application techniques such as spin coating.
Currently, polyimide resins are one class of materials which are employed as thin film dielectrics in the electronics industry. However, polyimide resins may absorb water and hydrolyze which can lead to circuit corrosion. Metal ions may migrate into the dielectric polyimide layer requiring a barrier layer between the metal lines and polyimide dielectric. Polyimides may exhibit poor planarization and gap fill properties. Non-fluorinated polyimides may exhibit undesirably high dielectric constants.
Kumar and Neenan, in Macromolecules, 1995, 28, pp 124-130, disclose numerous polyphenylenes made from biscyclopentadienones and bisacetylenes. They teach that the polyphenylenes have potential as photodefineable organic dielectrics. Wrasidlo and Augl, in J. Polym. Sci., Part B (1969), 7(7), 519-523, disclose the copolymerization of 1,4-bis(phenylethynyl)benzene with 3,3'-(1,4-phenylene)-bis(2,4,5-triphenylpentadienone). They report a soluble, yellow, infusible polymer was obtained.
The materials described in Kumar and Wrasidlo are soluble but may not be suitable for some uses such as spin coating to fill gaps because the materials were polymerized to exhaustion of the cyclopentadienone moieties which provides relatively high molecular weights. The molecular weight may be too high to permit application by spin coating over a patterned surface containing gaps to be filled by the dielectric. Based on the reported glass transition temperatures, such materials may not be able to withstand the processing desired for interlayer dielectrics in integrated circuits.
In U.S. Pat. Nos. 5,334,668; 5,236,686; 5,169,929; and 5,338,823, Tour describes several methods of preparing cross-linkable polyphenylene compositions for the preparation of glassy carbon. The polyphenylenes are made by polymerizing 1-bromo-4-lithiobenzene to form a brominated polyphenylene and then coupling substituted phenylacetylenes, such as phenylacetylenyl phenyl acetylene, to the residual bromines. The polyphenylenes have melting points around 200.degree. C. prior to crosslinking.
It would be desirable to provide a polymer dielectric to the microelectronics fabrication industry which provides a reliably low dielectric constant, high thermal stability and a high glass transition temperature and which preferably, permits application by spin coating to planarize and fill gaps on a patterned surface.